1. Field of the Invention
The invention relates to an electromagnetic wave detector made of a semiconductor material with quantum well structure, notably a detector that can be used for the detection of shorter wavelengths than those detected by known detectors.
2. Description of the Prior Art
The rapid advances made in the field of epitaxial growth on GaAs substrates have enabled the development of a new class of electromagnetic wave detectors using intraband transitions in quantum wells as shown in FIG. 1 and described in the document by E. ROSENCHER and P. Bois, Physical Review, B44, 11315 (1991).
The recent development of the performance characteristics of components of this type is related in particular to the fact that it is relatively easy to make multilayers of heterojunction semiconductors in the standard system of molecular beam epitaxy (MBE), i.e. the GaAs/Ga.sub.1-x Al.sub.x As system. By adjusting the growth parameters, the thickness of the quantum wells and the percentage x of aluminum in the barriers that dictate the confinement potential, it is possible to choose to center a narrow band (about 1 .mu.m) of detection on a given wavelength (see FIG. 2). However, the use of the standard GaAs.sub.1-x Al.sub.x As system with 0.ltoreq.x.ltoreq.43% entails a restriction, in terms of wavelength, to the 7-20 .mu.m range. To overcome this restriction, and in particular to extend the scope of the device towards the 3-5 .mu.m band, several approaches have been envisaged.
The first approach consists of increasing the percentage of aluminum of the barrier to over 43%. However, although this approach makes it possible to obtain materials with "standard" growth conditions, it is not optimal for reasons related to the band structure of the III-V type materials. Indeed, increasing the value of x amounts to increasing the confinement potential and hence the optical excitation energy but, because of the intersection of the X and F bands (see FIGS. 3a to 3c), the thermal excitation energy remains low (of the order of 120 meV). For this reason, the detector shown in FIG. 4 will effectively have an optical response in the 3-5 .mu.m range, but with the signal-to-noise ratio and hence the BLIP temperature of a multiple quantum well detector working in the 8-12 .mu.m range, i.e. T.sub.BLIP .apprxeq.70 K.
The second approach consists of deliberately choosing other pairs of III-V semiconductors such as GaInAs/AlInAs epitaxially grown on InP by MOCVD. This choice can be used to obtain components of optimal quality from the viewpoint of the intrinsic limitations, but has the disadvantage of using technologies that are less conventional and hence more difficult to implement.
The aim of this invention is to slightly modify the system of materials used so that it remains close to the MBE standard and is therefore easy to make.